1. Field of the Invention
The present invention relates to fuel supply devices, and in particular to in-tank fuel supply devices installed within fuel tanks for supplying fuel to internal combustion engines.
2. Description of the Related Art
An in-tank fuel supply device generally includes a fuel pump for pumping a fuel from a fuel tank, a fuel filter surrounding the fuel pump and having a filter case with a filter element disposed therein, a reservoir cup (sub-tank) that receives the fuel pump and the fuel filter therein, and a set plate (flange) vertically slidably mounted to the reservoir cup and fixed in position relative to the fuel tank. This type of fuel supply device is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2005-83303. In this publication, a circular adaptor (support member) extends inwardly from the inner circumferential wall of a fuel filter and resiliently supports a fuel pump in a suspending manner. A discharge port of the fuel pump and a fuel inlet port of the fuel filter are connected to each other via a first tube, such as a rubber hose. A fuel outlet port of the fuel filter and a fuel discharge pipe of the set plate are connected to each other via a second tube, such as a rubber hose. The fuel filter has a surplus fuel discharge pipe. The surplus fuel discharge pipe extends from the lower side of the fuel filter and is fixedly mounted to the reservoir cup by press-fitting the surplus fuel discharge pipe into a boss portion of the reservoir cup. A spring is interleaved between the fuel filter and the set plate for biasing the reservoir cup in a direction toward the bottom of the fuel tank via the fuel filter. The set plate has two shafts extending downward from the bottom surface. The two shafts are vertically slidably inserted into corresponding two cylindrical shaft guides disposed at the upper end of the side wall of the reservoir cup. The two shafts have the same diameter, and therefore, the shaft guides have the same inner diameter and the same vertical length. In other words, the distance between the axes of the two shafts is equal to the distance between the axes of the two shaft guides.
Also, Japanese Laid-Open Publication No. 2004-138046 discloses a fuel supply device having the construction that is basically the same as the Publication No. 2005-83303 but is different from this publication in the configurations of the shaft guides. Thus, according to the Publication No. 2004-138046, shaft guides are formed integrally with a reservoir cup and each includes three recesses formed in the inner circumferential surface thereof in order to divide the inner circumferential surface into three segments distributed equally in the circumferential direction. With this arrangement, even in the event that shafts extending from a set plate have inclined relative to and within the corresponding shaft guides, the shafts do not contact the inner circumferential surfaces of the shaft guides at positions of the recesses. Although the outer diameter of the shafts and the inner diameter of the shaft guides are the same with each other, the shaft guides have different vertical lengths.
By the way, the fuel within the reservoir cup is drawn into the fuel pump and is then supplied from the discharge port of the fuel pump to an internal combustion engine under pressure via the first tube, the fuel filter, the second tube and the fuel discharge pipe of the set plate in this order. During the pumping operation of the fuel, the fuel pump may vibrate as it is driven. If vibrations of the fuel pump are seriously transmitted to the fuel filter or the reservoir cup, a loud vibration sound may be produced. Therefore, according to the Publication No. 2005-83303, in order to reduce the vibration sound, a plurality of vibration damping members having both flexibility and slidability are disposed between the fuel pump and the fuel filter. The vibrations of the fuel pump may be absorbed and damped by the vibration damping members, and hence, vibrations that may be transmitted to the fuel filter and the reservoir cup may be reduced.
Vibrations may be transmitted from the reservoir cup to the set plate also via contact portions between the shafts and the shaft guides. The sizes of the shafts and the shaft guides are typically designed such that a small clearance is ensured between each shaft and the corresponding shaft guide. Therefore, if the shafts are assembled such that each shaft is positioned vertically centrally within the corresponding shaft guide, no direct contact may occur between the shafts and the shaft guides. However, practically, the positional relationship between the set plate and the reservoir cup may change or the shafts may incline due to error in the assembling operation, vibrations of a vehicle produced during the running of the vehicle, flexure of the fuel tank by the pressure of the fuel within the fuel tank, etc. In such a case, the shafts may contact the shaft guides to cause transmission of vibrations via the contact portions. In the case of the Publication No. 2004-138046, the shafts and the shaft guides may not contact each other at positions of the recesses formed in the inner circumferential surface of each shaft guide. Therefore, vibrations may not be transmitted when the shafts have inclined in the directions toward the recesses.
With the arrangement of the Publication No. 2005-83303, although transmission of vibrations between the fuel pump and the fuel filter may be reduced, it is not possible to completely prevent transmission of vibrations between these components. In addition, transmission of vibrations from these components, i.e., transmission of vibrations from the fuel filter to the reservoir cup or the set plate, is not taken into account in this publication. Thus, vibrations may be transmitted to and from the fuel pump, the fuel filter, the reservoir cup and the set plate via connecting members or connecting portions (fixing portions) between these components. More specifically, vibrations may be transmitted from the fuel filter to the reservoir cup or the set plate via the second tube connecting between the fuel outlet port of the fuel filter and the fuel discharge pipe of the set plate, the spring interleaved between the fuel filter and the set plate, and the fixing portions between the fuel filter and the reservoir cup. In addition, as noted above, vibrations may be transmitted to the set plate via contact portions between the shafts and the shaft guides. Further, vibrations may be transmitted from the fuel pump to the fuel filter via the adaptor (support member) of the fuel filter that resiliently supports the fuel pump in suspending manner, and via the first tube that connects between the fuel discharge port of the fuel pump and the fuel inlet port of the fuel filter.
Further, with the fuel supply device of the Publication No. 2005-83303, there is no regularity in the positional relationship between connecting members or connecting portions that connect the fuel pump, the fuel filter, the reservoir cup and the set plate to each other. The positional relationship may influence the direction of vibrations of the fuel filter, etc. Therefore, the directions of vibrations or impact forces applied to the connecting members or the connecting portions are not uniform, and hence, the fuel pump, i.e., a source of vibrations, and the fuel filter positioned on the upstream side with respect to the direction of transmission of vibrations are hard to move. As a result, vibrations may be transmitted from the fuel pump to the fuel filter due to incomplete absorption by the vibration damping members and may be transmitted further to the reservoir cup and the set plate. In addition, due to no regularity in the positional relationship between the connecting members or the connecting portions, the connecting members or the connecting portions may rather serve as stays against vibrations. Therefore, the rigidity of the fuel filter with respect to the direction of vibrations may be increased (i.e., the amplitude of vibrations may be reduced), and hence, a possibility may exist that vibrations may be transmitted with increased energy. Also in the arrangement of the Publication No. 2004-138046, there is no regularity in the positional relationship between the connecting members or the connecting portions, and therefore, the arrangement of the Publication No. 2004-138046 involves the same problems as described above.
Further, with the arrangement of the Publication No. 2005-83303, the shafts have the same diameter and the shaft guides also have the same diameter. Therefore, if the positional relationship between the set plate and the reservoir cup has been changed of if the set plate and the reservoir cup have inclined relative to each other, both shafts may contact their respective shaft guides, and therefore, the contact area between the shafts and the shaft guides is large. Hence, transmission of vibrations between the shafts and the shaft guides may increase. In the case of the arrangement of the Publication No. 2004-138046, it is possible to avoid contact between the shafts and the shaft guides in some directions by the recesses formed in the inner circumferential surfaces of the shaft guides. The positions of the recesses in each shaft guide are determined not to oppose to each other in the diametrical direction to enhance the function of avoiding the contact. However, it is not possible to cope with the offset or inclination in directions along which no recess is formed. In this case, the shafts may contact the shaft guides by a large contact area and the transmission of vibrations may increase. Although the shaft guides of the Publication No. 2004-138046 have different vertical lengths from each other, this arrangement of this publication does not serve to reduce the contact area between the shafts, and therefore, transmission of vibrations between these components may not be reduced.
Therefore, there is a need in the art for fuel supply devices that can reduce transmission of vibrations from a fuel pump to a reservoir cup or a set plate.